Seasonal Exchange of Bottlenose Dolphins Resident to the Outer Banks of North Carolina

Elizabeth Mason1, 2

and Jessica Taylor1

1Outer Banks Center for Dolphin Research

2Duke University

Background

Bottlenose dolphins (Tursiops truncatus) can be found worldwide, in warm temperate

waters (Leatherwood and Reeves 1983). In the Western North Atlantic, these populations are

separated into two different distinct ecotypes, coastal and offshore. Within those two distinct

ecotypes, individuals can display seasonal residency (Toth-Brown and Hohn 2007), year round

residency (Pryor and Norris 1991) and transience (Defran and Weller 1999), and the type of

residency can depend on protection from predators, food availability, and nursery usage, as well

as many other biotic and abiotic factors (Miller et al. 2013). To better manage these populations

under the Marine Mammal Protection Act (MMPA), a better understanding of the differences

between stocks should be established. Determining a better understanding of population

structure and stock size will allow for better management plans and long term protection.

In 1997, the Mid-Atlantic Bottlenose Dolphin Photo-identification Catalog (MABDC)

was developed in order to better understand bottlenose dolphin stock structure on the Western

North Atlantic coast (Urian 2014). The MABDC is a collection of photo-identification research

from different locations along the Atlantic coast. Contributors submit data to the MABDC,

allowing the data to be shared among individuals and available online. The MABDC is one

centralized, comprehensive location for sightings of bottlenose dolphins, which allows for more

streamlined, efficient, and widespread research to be completed.

The Northern North Carolina Estuarine System (NNCES) stock of bottlenose dolphins, as

defined by the NOAA-NMFS (Waring et al. 2014), occurs from southern Virginia to southern

North Carolina. The NNCES includes individuals that use the estuarine waters of the Pamlico

Sound from Beaufort, NC to southern Virginia and the lower Chesapeake Bay and coastal waters

up to 1 km from shore from early May until late October. In the cooler months (November-

April), animals within the NNCES stock migrate south to the coastal waters (within 3 km of

shore) between the New River and Cape Hatteras, NC (Waring et al. 2014).

The bottlenose dolphin population in Roanoke Sound, NC, which is included in NNCES,

has been monitored since 1997 (Taylor et al. 2014). By using photo identification methods,

distinguishable individuals are tracked over time to collect information on population trends that

can contribute to the stock assessment. Photo identification is a type of mark and recapture study

used to monitor bottlenose dolphins (Weir et al. 2008). The identification process is dependent

on clear images of natural markings on the dorsal fins of the cetaceans. This study was initially

started by the Nags Head Dolphin Watch, and eventually taken over by the Outer Banks Center

for Dolphin Research (OBXCDR) in 2008.

The purpose of this study was to examine the movement patterns of individuals with high

site fidelity to Roanoke Sound, NC, specifically, whether these frequently seen individuals travel

to Beaufort, NC. This assessment can be utilized to better define the NNCES stock and to better

guide management recommendations and practices.

Methods

Data Collection

The study area (Figure 1) is located in the Roanoke Sound of the Outer Banks,

approximately 41 square miles. The study area spans from the northern tip of Roanoke Island

south to Oregon Inlet. Roanoke Sound is the body of water that separates Nags Head from

Roanoke Island. This body of water has many recreational uses as well as important value as a

commercial fishing area.

Figure 1: Roanoke Sound Study Area

The OBXCDR regularly conducts both dedicated and opportunistic photo-identification

surveys of bottlenose dolphins within the study area. Dedicated exploratory surveys were

conducted in the southernmost area of the study site during October 2007. Dedicated photo-id

surveys were conducted from June 2008 - August 2008, February 2009, May 2009-October

2009, May 2010-October 2010, and May 2011-October 2011. In November 2011, a standardized

transect route was designed to cover the entire study area. Dedicated transect surveys were

conducted at least once a month in the study area during November 2011, April 2012-November

2012, and April 2013-November 2013.

All dedicated surveys were conducted from a 16’ or 17’ outboard vessel in the study area,

with the exception of May and July 2013, due to bad weather and boat problems. The

standardized transect route was made in the program MapSource and uploaded to a hand held

GPS unit that is taken on each survey. During the dedicated survey, when dolphins are sighted,

the location was marked on the GPS unit and the dolphins were slowly approached in order to

not affect their natural behavior. Additional information including the estimated number of

dolphins per group, date, time, activity state, observed behaviors, and environmental conditions

such as salinity, water temperature, and visibility, sightability, and cloud cover, was collected for

each sighting. Photographs of the dorsal fins of each dolphin were obtained using standard

photo-identification techniques (Wursig and Wursig 1977). Sightings were concluded when one

of four things happened: If the dolphins exhibited avoidance behavior, the dolphins were lost, the

sighting lasted the limit of one hour according to the General Authorization permit under which

the surveys were conducted, or all of the dorsal fins within the group were photographed. At the

end of each sighting, the vessel would return to the transect where the sighting had started and

would continue along the transect until another group was seen or until the transect route was

completed.

The opportunistic data was collected from May 2008-October 2013 aboard the Nags

Head Dolphin Watch. The collection of data and survey methods were similar to the dedicated

survey methods. However, the route differed in locating dolphins, in that a specific transect was

not utilized, dolphin approaches were further away, and sightings were conducted under the

National Marine Fisheries Service (NMFS) Recommended Viewing Guidelines for bottlenose

dolphins for the southeast region. In order to observe how effort has varied over the years, the

number of surveys and the number of sightings has been recorded (Figure 2).

Figure 2: OBXCDR Dedicated and Opportunistic Survey effort

The program FinBase (Adams et al. 2006) was used in the processing of the sighting data

and photo-identification images. Images collected from dedicated surveys and opportunistic

surveys were sorted, graded for photo quality, and linked to the sighting data by matching to the

OBXCDR photo-identification catalog. For every fin matched to the catalog another individual

verified the match, to ensure that every match had two researchers validating the match. The data

were then sent to Kim Urian, Duke University Marine Lab, in order for it to be added to the

MABDC. The OBXCDR catalog includes dorsal fins from October 2007 – July 2014.

In order to examine population estimates and trends, a Bayesian mark-recapture approach

was (Durban et al. 2010) applied to 413 dolphins that were identified from high quality images

with high and average distinctiveness (Taylor et al. 2016). This methodology was utilized to

identify clusters with different levels and patterns of capture probability over time (Gardner et al.

2010; Fearnbach et al. 2012). Three different clusters were established with Clusters 2 and 3

having relatively high site fidelity to Roanoke Sound (Taylor et al. 2016). These 59 individuals

were matched to the North Carolina Maritime Museum Catalog (Table 1) using the MABDC.

Every match was verified by Keith Rittmaster or Nan Bowles (the contributors for the NCMM),

Jessica Taylor of the OBXCDR, and Kim Urian.

Table 1: MABDC catalogs used in comparisons.

Field Site Catalog

Size (approx)

Period Primary Contact Organization

Roanoke Sound, NC 330 2007-2013 Jessica Taylor OBX Center for Dolphin Research

Beaufort, NC 2456 1985-2015 Keith Rittmaster NC Maritime Museum

The NCMM catalog was selected because it is close to the southern most location of the

NNCES. Understanding the exchange between these two locations could give better definition of

the stock.

0

20

40

60

80

100

120

2008 2009 2010 2011 2012 2013

Co

un

t

Year

Field Effort

Surveys

Sightings

Results

Table 2 shows the matched dolphins from cluster 2 of the OBXCDR catalog to the NCMM

catalog. Once matched, the demographics from the OBXCDR catalog were collected to allow for

more in depth analysis. Females were determined by a minimum of 3 sightings with a dependent

calf. Males were determined by a minimum of 3 sightings with the same adult.

Table 2: Cluster 2 matched dolphin demographics from OBXCDR catalog

ALIAS NUMBER

OBX SIGHTINGS

OBXCDR ID

NCMM ID

GENDER

YEARS SINCE FIRST

OBX SIGHTING

MOST RECENT

SIGHTING

Artemis 17 6 1489a female 9 5/29/2012 Knobby Top 17

15 0938a probably female 9 6/27/2014

FB717 15 33 1342a female 9 5/23/2014

5 81 3350a unknown 8 6/23/2010

Four 10 83 1915p unknown 8 6/25/2014 Jess squared 11

242 2320a female 8 9/15/2011

FB459 9 247 1882a female 8 7/13/2014

10 283 1596p unknown 8 8/11/2013

6 287 1828p unknown 8 9/12/2012

12 386 4048a unknown 8 6/28/2012

7 728 0149a unknown 6 10/30/2011

Eleven out of twenty-eight were matched to the NCMM catalog. The remaining seventeen

individuals were not found in the NCMM catalog (Figure 3).

Figure 3: Matching results of dolphins in cluster 2 to the NCMM catalog

Table 3: Cluster 3 matched dolphin demographics from OBXCDR catalog

ALIAS NUMBER

SIGHTINGS OBXCDR

ID NCMM

ID GENDER

YEARS SINCE FIRST

SIGHTING

MOST RECENT SIGHTING

Mohammed 29 1 0618a male 9 6/27/14

Onion 33 7 0026a male 9 6/27/14

Pinchers** 28 8 0271a male 9 6/22/12

Buddha** 27 9 1142a male 9 8/11/13

Madi 16 12 0465a female 9 6/27/14

Sprite 34 13 0344a probably male 9 7/13/14

Skylar 40 18 1019q male 9 6/27/14

13 78 2399a unknown 8 6/25/14

Lilo 38 90 2013a probably male 8 6/25/14

Vidalia 19 109 3541p probably female 8 10/3/09

Rake 37 112 2087a Probably male 8 6/27/14

Rainbow 29 126 2573a male 8 6/27/14

Moose 28 128 0242q unknown 8 8/20/13

Fatlip 20 315 0173a female 8 6/28/12

FB708 27 317 1356a male 8 6/25/14

Sequoia 30 318 1188a male 8 6/27/14

3 503 3944a unknown 7 9/26/09

Flounder 11 531 3338a probably female 6 6/27/14

Curly** 18 553 4027a probably male 7 10/16/13

Sinatra 19 570 3906a female 8 8/20/13

39.29%

60.71%

Cluster Two

Matched

NotMatched

**deceased

Twenty out of thirty-one were successfully matched to the NCMM catalog. The remaining

eleven were not found in the NCMM catalog (Figure 4).

Figure 4: Matching results of dolphins in cluster 3 to the NCMM catalog

Tables 2 and 3 show the matched dolphins from cluster 2 and 3 (respectively) of the

OBXCDR catalog to the NCMM catalog. Once matched, the demographics from the OBXCDR

catalog were collected to allow for more in depth analysis, From those demographics we were

able to assess the gender of the matched dolphins and establish if there was a difference between

the genders of the matched dolphins (Figure 5). Gender did not seem to influence whether

individuals were sighted in both study areas.

Figure 5: Gender for all matched dolphins from the OBXCDR catalog information.

**Probably male and probably female included in male and female, respectively.

64.52%

35.48%

Cluster Three

Matched

NotMatched

32.26%

38.71%

29.03%

Total Gender

Female

Male

Unknown

Figure 6: Cumulative matching results of cluster 2 and 3. In total, thirty-one out of a potential

fifty-nine were matched.

In order to establish if non-matched dolphins from Clusters 2 and 3 were present in the

Beaufort area, we checked the MABDC for previously made matches to other Beaufort area

catalogs. Tables 4 and 5 show the results from this analysis. “Maybe” is used for matches

pending in the MABDC, showing that a potential match has been suggested.

CatalogID Alias Cluster NCMM

Matched to other Beaufort,

NC Catalog?

63 Lisa Caroline 2 NO MATCH

maybe

77 2 NO MATCH no 103 2 NO MATCH no 104 Easy 2 NO MATCH maybe

127 2 NO MATCH no

131 2 NO MATCH no 168 2 NO MATCH no 221 2 NO MATCH no 237 Emma 2 NO MATCH no 285 2 NO MATCH no

289 2 NO MATCH no 393 2 NO MATCH no

52.54%

47.46%

Total

Matched

NotMatched

498 2 NO MATCH no

541 2 NO MATCH no 702 2 NO MATCH no 737 2 NO MATCH no 818 2 NO MATCH no

Table 4: Unmatched NCMM cluster 2 dolphins

MABDC cluster two unmatched dolphins were checked to see if they matched to other

Beaufort area catalogs. Two of the seventeen were potential matches, still waiting for

verification from researchers.

CatalogID Alias Cluster NCMM

Matched to other

Beaufort, NC

Catalog?

52 Lorna 3 NO MATCH maybe 54 3 NO MATCH no

116 3 NO MATCH no

130 Double Scoop 3 NO MATCH no

135 3 NO MATCH no 240 Kerner 3 NO MATCH no 246 Rocky 3 NO MATCH yes 281 Winnie 3 NO MATCH no 364 FB457 3 NO MATCH yes 561 Cola 3 NO MATCH no 648 Nick 3 NO MATCH no

Table 5: Unmatched NCMM cluster 3 dolphins

MABDC cluster three unmatched dolphins were checked to see if they matched to other

Beaufort area catalogs. Two of the eleven were matched and one was a potential match still

waiting for verification from researchers.

Using demographic data from Tables 2 and 3 we looked to see if there was a significant

difference in the number of years since first sighted. This was to check and see if there was a

correlation between being seen earlier and being seen more frequently (eg placement in cluster).

These results show that there is no difference between years since first sighting (Figure 7). This

suggests that there is not a relationship between years since first seen and probability of being

seen.

Figure 7: The average number of years since first sighting.

Discussion

Over half of the cluster two dolphins were not matched to the NCMM catalog, (Figure 3).

However, nearly 65% of the cluster three dolphins were matched (Figure 4). Cluster two

dolphins are less likely to be sighted in both Roanoke Sound as well as near Beaufort NC, than

the cluster three dolphins. When the cluster two and cluster three were combined, the matched

were slightly greater than the unmatched (Figure 6). Dolphins in cluster three likely occur in the

Beaufort area, as well as within the Roanoke Sound, while cluster two dolphins are may be more

transient within the Beaufort area.

To further examine this, we also used the MABDC to check whether any of the

unmatched dolphins from cluster two or three were previously matched to any other Beaufort

area catalogs (Tables 4 and 5). These results show that cluster three was slightly more likely to

be matched to other Beaufort catalogs. Cluster 3 had 27.27% potentially matched to other

catalogs and cluster 2 had only 11.76% potentially matched. This comparison supports our

hypothesis that cluster 3 dolphins are more likely to be sighted within the Beaufort area, than

cluster 2 dolphins.

As demonstrated by Figure 5 there was no significant difference in gender, which suggest

that there is very little influence of gender on occurrence patterns. Slightly more males were

matched; however overall there were an equal proportion of male, female, and unknown

dolphins matched between the catalogs. These results could suggest that both males and females

use the study area with similar frequency. This finding is corroborated by Rossbach and Herzing

(1999) where they identified two communities with high sight fidelity, each with no significant

difference in gender, suggesting that these results might be typical behavior for estuarine

bottlenose dolphins of both genders.

The average number of years since first sighting was compiled to determine if dolphins

seen within Roanoke Sound for a longer period of time were more likely to be matched to

NCMM catalog (Figure 7). There was very little difference between the clusters, suggesting that

the number of years since they were first sighted has no effect on determining occurrence

8.09 8

0.001.002.003.004.005.006.007.008.009.00

10.00

Cluster 2 Cluster 3

Average number of years since first sighting

Average number of years sincefirst sighting

patterns. As this study continues and the clusters change it will be important to observe whether

or not the years since first sighting has an impact on the sight fidelity or occurrence patterns.

Future studies can potentially look at the relationships between individuals with high

sighting probability in Roanoke Sound. Dinis et al. (2016) suggests that there are certain

individuals within populations that facilitate relationships between resident and transient

dolphins. While the loss of these individuals would probably not have an immediate effect on the

social structure, it is thought that they facilitate genetic flow (Quérouil et al. 2007).

Understanding social structure is necessary in ensuring a healthy population of dolphins.

Comparisons between Virginia and New Jersey catalogs to the OBXCDR catalog within

the MABDC can be examined to help understand whether cluster two and three individuals occur

in other locations. This research can help understand if the “resident” dolphins in the Roanoke

Sound are considered transient in other locations. This information can help researchers

understand and possibly better definite the NNCES, as well as understanding where and when

dolphins may be found in certain areas. This research will only be possible through collaboration

with other researchers as sighting records or histories for other catalogs would be necessary

through contribution to the MABDC. Understanding, more definitively, where dolphins spend

their time could help establish the range and a seasonal habitat and therefore also better help

establish the range of the NNCES. Furthermore, by better establishing how many individuals are

in an area at a given time measures can be taken to protect their populations or to make

recommendations for events that might potentially impact their conservation.

Works Cited

Adams, J.D., Speakman, T., Zolman, E., and L.H. Schwacke. 2006. Automating Image

Matching, Cataloging, and Analysis for Photo-Identification Research. Aquatic Mammals

32(3): 374-384.

Defran, R. H. and D. W. Weller. 1999. Occurrence, distribution, site fidelity and school size of

bottlenose dolphins (Tursiops truncatus) off San Diego, California. Mar. Mamm. Sci.

15:366-380.

A Dinis, F Alves, C Nicolau, C Ribeiro, M Kaufmann, A Cañadas & L Freitas (2016) Bottlenose

dolphin Tursiops truncatus group dynamics, site fidelity, residency and movement

patterns in the Madeira Archipelago (North-East Atlantic), African Journal of Marine

Science, 38:2, 151-160, DOI: 10.2989/1814232X.2016.1167780

Durban, J., D. Ellifrit, M. Dahlheim, J. Waite, C. Matkin, L. Barrett-Lennard, G. Ellis, R.

Pitman, R. DeLuc, and P. Wade. 2010. Photographic mark-recapture analysis of clustered

mammal-eating killer whales around the Aleutian Islands and Gulf of Alaska. Marine

Biology 157: 1591-1604.

Fearnbach, H., J. Durban, K. Parsons, and D.Claridge. 2012. Photographic mark-recapture

analysis of local dynamics within an open population of dolphins. Ecological

Applications 22(5): 1689-1700.

Gardner, B., J. Reppucci, M. Lucherini, and J.A. Royle. 2010. Spatially explicit inference for

open populations: estimating demographic parameters from camera-trap studies. Ecology

91: 3376-3383.

Gelman, A., X. Meng, and H. Stern. 1996. Posterior predictive assessment of model fitness via

realized discrepencies. Statistica Sinica 6: 733-759.

Leatherwood S, Reeves RR (1983a) The Sierra Club handbook of whales and dolphins. Sierra

Club Books, San Francisco

Lunn, D.J., A. Thomas, N. Best, and D. Spiegelhalter. 2000. WinBUGS-a Bayesian modelling

framework: concepts, structure, and extensibility. Statistics and Computing 10: 352-337.

Miller, L. J., Mackey, A. D., Solangi, M., & Kuczaj, S. A. (2013). Population abundance and

habitat utilization of bottlenose dolphins in the Mississippi Sound, 151(September 2012),

145–151. http://doi.org/10.1002/aqc.2278

Pryor, K., & Norris, K. S. (1991). Dolphin societies: Discoveries and puzzles. Berkeley:

University of California Press.

Quérouil S, Silva MA, Freitas L, Prieto R, Magalhães S, Dinis A. 2007. High gene flow in

oceanic bottlenose dolphins (Tursiops truncatus) of the North Atlantic. Conservation

Genetics 8: 1405–1419.

Rossbach, Kelly A., Herzing, Denise L. Inshore and offshore bottlenose dolphin (Tursiops

truncatus). Canadian Journal of Zoology; Apr 1999; 77, 4; ProQuest pg. 581 Inshore and

offshore bottlenose dolphin (Tursiops truncatus)

Taylor, B.L., “Defining “population” to meet management objectives for marine mammals.”

Molecular Genetic of marine mammals. Special Publication No. 3. The Society of Marine

Mammology. (1997): 46-65. (look up taylor 2007

http://onlinelibrary.wiley.com.proxy.lib.duke.edu/doi/10.1111/j.1748-

7692.2003.tb01317.x/epdf)

Taylor, J., H. Fearnbach, and J. Adams. 2016. Use of clustered mark-recapture methods to

monitor bottlenose dolphins (Tursiops truncatus) in the Outer Banks, NC. Poster

presentation at the Southeast and Mid-Atlantic Marine Mammal Symposium, 1-3 April

2016, Savannah State University, Savannah, GA.

Taylor, J., Hart, L., Krumsick, H., and J. Adams. 2014. Preliminary Examination of Skin Lesions

on Bottlenose Dolphins (Tursiops truncatus) in the Outer Banks, North Carolina. Poster

presentation at the Southeast and Mid-Atlantic Marine Mammal Symposium, 28-30

March 2014, University of North Carolina Wilmington, Wilmington, NC

Toth-Brown, J., and A. A. Hohn. 2007. Occurrence of the barnacle, Xenobalanus globicipitis, on

coastal bottlenose dolphins (Tursiops truncatus) in New Jersey. Crustaceana 80:1271–

1279

Torres, L. G., Rosel, P. E., D'agrosa, C., and Read, A. J. "Improving Management of

Overlapping Bottlenose Dolphin Ecotypes Through Spatial Analysis And Genetics."

Marine Mammal Sci Marine Mammal Science 19.3 (2003): 502-14. Web.

Urian, K. 2014. Stock Identity of Stranded Bottlenose Dolphins with Evidence of Fisheries

Interaction in Virginia, North Carolina, and South Carolina. Final Report to North

Carolina Sea Grant: Bycatch Reduction Marine Mammal Project 12-DMM-02, 26 pp.

Waring G.T., E. Josephson, K. Maze-Foley, and P.E. Rosel, editors. 2014. U.S. Atlantic and

Gulf of Mexico Marine Mammal Stock Assessments -- 2013. NOAA Tech. Memo.

NMFS-NE-228. Weir, Caroline R., Sarah Canning, Kevin Hepworth, Ian Sim, and Karen

A Stockin. "A Long-Term Opportunistic Photo-Identification Study of Bottlenose

Dolphins (Tursiops Truncatus) off Aberdeen, United Kingdom: Conservation Value and

Limitations." Aquatic Mammals Aquatic Mammals (2008): 436-47. Print.

Würsig, B. and M. Würsig. 1977. The photographic determination of group size, composition

and stability of coastal porpoises, Tursiops truncatus. Science 198:755-756.